Electric field induced tunable bistable conductance switching and the memory effect of thiol capped CdS quantum dots embedded in poly(methyl methacrylate) thin films

Abstract

Experimental results on conductivity switching and appearance of hysteresis in the current–voltage characteristics of thiol (benzyl mercaptan)-capped CdS quantum dots (QDs) embedded in a poly(methyl methacrylate) (PMMA) matrix are presented in this manuscript. The dependence of switching behavior has been studied under different conditions such as sample cell temperature, scan speed of voltage, illumination of light of various intensities, film thickness, size of thiol-capped CdS QDs etc. The voltage at which the conductivity switching occurs i.e. threshold voltage (V_th) appearing in the current–voltage characteristic curve, decreases with the increasing sample cell temperature and also with increasing intensity of photoexcitations but V_th increases with the increasing scan rate of voltage and size of thiol-capped CdS QDs. Between forward and reverse bias sweeps, the switching events exhibit hierarchy of hysteresis loops. The area within the hysteresis loops decreases with increasing sample cell temperature and ultimately disappear at higher temperatures. The switching events can be tuned by changing the external parameter (experimental conditions) such as sample cell temperature, scan speed of bias voltage, irradiation of light, size of thiol-capped CdS QDs etc. The switching mechanism and appearance of hysteresis have been attributed to an electric field-induced charge transfer from the polymer to the thiol-capped CdS QDs. The nanocomposites of PMMA and thiol-capped CdS nanocrystallites may be suitable for polymer based memory devices.